WASHINGTON — Not long ago, Allen St. Pierre couldn’t get an audience with many politicians. When he tried to send them campaign contributions, the checks were returned. His efforts to persuade the political establishment to take seriously the legalization of marijuana were met with blank stares, or worse.

But now lawmakers are beating a path to his door for meetings and advice, hoping to harness this new energy behind an issue that had been on the fringe of American politics. The once-quixotic goal of St. Pierre’s group — NORML, the National Organization for the Reform of Marijuana Laws — is now one of Washington’s most-discussed issues.

Representatives of an array of potential presidential candidates have contacted him, asking for meetings to seek NORML’s endorsement and tap its donor base. Campaign checks are being cashed at a greater rate.

“We’re no longer talking about whether marijuana should be legal, [but] about when it should be legal,” St. Pierre said.

It is a dizzying degree of change in a relatively short time. “I ask the staff every day to nonsexually pinch me,” St. Pierre said. “You have to remind yourself how far we’ve come.”

The signs of a shifting political environment are hard to miss. President Obama, who famously revealed he had smoked pot in his high school “Choom Gang,” said in an interview published last month that marijuana was no more dangerous than alcohol.

Colorado and Washington state have legalized recreational marijuana.

‘If you present yourself as counterculture, you’ll be treated as counterculture. I’m a preppy New Englander who wears tweed.’

Twenty states, including Massachusetts, make cannabis legal for medical use, and a number of others, also including Massachusetts, are preparing ballot initiatives or legislation that would authorize recreational purchases.

If you were to cast for an affable, clean-cut New Englander, St. Pierre would surely get the part. His salt-and-pepper hair is trimmed neatly above his ears. On a recent day, he wore navy slacks, loafers, and a V-neck sweater over a green flannel shirt. The 48-year-old from Chatham used to be a caddy for the late House speaker Thomas P. “Tip’’ O’Neill.

There’s just one thing: His office, which is on K Street about two blocks from the White House, is a practically a museum to marijuana. There’s marijuana leaves on T-shirts and hats, candles that look like joints, and the latest issue of High Times magazine. A marijuana plant sits on his desk, and a giant joint on a bookshelf (both are fake).

High Times, indeed.

With the march toward legalization begun, there is much to be decided in Washington. Obama’s recent comments effectively cast the issue as “Who will sell it, who will get rich from it.” said St. Pierre.

He would not reveal which prospective presidential candidates have contacted his organization, but he did note that no one from Hillary Clinton’s network has reached out — though he suspects they will as public opinion continues to move in his direction.

In October, nearly 60 percent of Americans said the drug should be legalized, the first time that a clear majority felt that way in a Gallup Poll. It was a jump of 10 percentage points from the previous year.

A CNN poll released last month had similar findings, with senior citizens, Republicans, and Southerners now the only large demographic groups still opposed to legalized marijuana. Sixty-two percent of Democrats and 59 percent of independents backed legalizing the drug, compared with 36 percent of Republicans.

With the vast majorities of Democrats and those between the ages of 18 and 34 in support of legalizing marijuana. Some Democratic consultants see the issue as a way to reenergize young voters who have soured on Obama. In Florida, Democrats are hoping a ballot initiative on medical marijuana will drive up turnout this November for their gubernatorial hopeful, Charlie Crist.

Alaska is expected to vote on legalizing marijuana in August, and Oregon is likely to follow in November.

In the Northeast, 60 percent of those surveyed by CNN supported legalizing marijuana, greater than any other region in the country. As a result, marijuana advocates are targeting New England, with plans to have the issue before voters or state lawmakers in almost every state by 2016.

The New Hampshire House last month became the first legislative body to approve a bill legalizing marijuana, although Governor Maggie Hassan has said she would veto the bill.

“There’s been more public dialogue about marijuana and marijuana policy than ever before,” said Mason Tvert, communications director for the Marijuana Policy Project, another group advocating for legalizing marijuana. “The more people talk about marijuana and more they hear about it, the more support we see for ending prohibition.”

Most Americans no longer believe that marijuana is physically harmful, psychologically harmful, or a gateway drug. About 35 percent of Americans now say that smoking marijuana is morally wrong, half what it was in 1987.

Enforcement is increasingly seen as both a waste of time and as unfair. There are also potential financial benefits to legalizing – and taxing – the drug.

“Maybe we should legalize,” Senator John McCain, the Arizona Republican, said at a town hall meeting last year. “We’re certainly moving that way as far as marijuana is concerned. I respect the will of the people.”

St. Pierre has been in a unique position to see the change. He was hired by NORML in 1991, less than a decade after President Reagan declared a “War on Drugs” and just before Bill Clinton admitted to using marijuana in college but quickly added, “I didn’t inhale.”

St. Pierre grew up in Chatham and graduated from the University of Massachusetts Amherst.

In the 1980s, while caddying at Eastward Ho Country Club in Chatham, he learned that O’Neill wasn’t the best golfer (“his weight was a hindrance”), and loved to sing Irish tunes and drink at the bar (“he would hold court at the Wayside Inn”). But what he really learned from the master of the House was the old maxim that “all politics is local” — advice that marijuana advocates have used with remarkable effectiveness.

“I saw him work local politics at the most retail level,” St. Pierre said of O’Neill. “He knew how to work with everyone, from the dishwashers to the elite in the country.”

When St. Pierre joined the marijuana movement, it was composed mostly of counterculture activists, with long hair and goatees. St. Pierre, in buttoned-up Washington, tried to promote a different image.

“If you present yourself as counterculture, you’ll be treated as counterculture,” he said. “I’m a preppy New Englander who wears tweed. I shave twice a day sometimes because I’m so conscious about it.”

Most days he wears a golden cannabis leaf on his lapel. In Washington, it gets mistaken for a Canadian maple leaf; in Denver it earns him free meals.

Even Obama has tentatively embraced some of the movement’s ideas – even though this directly contradicts his administration’s stated policy that it “steadfastly opposes legalization of marijuana.”

“I don’t think it is more dangerous than alcohol,” Obama said in an interview with the New Yorker.

While Obama still characterized it as “a vice” and said he told his daughters it’s “a waste of time, not very healthy,” he also suggested current law is too harsh and it was “important” for the Colorado and Washington laws to move forward.

“We should not be locking up kids or individual users for long stretches of jail time when some of the folks who are writing those laws have probably done the same thing,” he said.

The White House has emphasized that Obama’s comments meant no shift in policy and said that he does not support nationwide decriminalization efforts.

Still, the administration policy can seem a bit muddled. While marijuana possession remains a felony, for example, the Justice Department said last year it will not prosecute such cases in states where it has been legalized.

Attorney General Eric Holder recently said the administration was working on regulations to make it easier for banks to work with state-sanctioned marijuana sellers. Banks have worried about being convicted on money laundering charges for dealing with an illegal narcotic, forcing marijuana sellers to deal entirely in cash.

Those opposed to legalizing marijuana have been promoting the ill effects of the drug, noting that it is stronger than when Obama was smoking it in the 1980s. Patrick Kennedy, the former Democratic Rhode Island congressman and chairman of Smart Approaches to Marijuana, has been calling for a tax on marijuana distributors that would be used to fund a study on impacts on young people.

“The insidiousness of marijuana is people think it isn’t having a negative impact on their life because it’s muted because of this type of drug,” Kennedy said in an interview. He said he tried to smoke marijuana but couldn’t because of his asthma. He has struggled with addiction to cocaine, Oxycontin, and alcohol.

St. Pierre, meanwhile, no longer is waging a lonely fight. Where there used to be two lobbyists on Capitol Hill arguing for legalized marijuana, St. Pierre said, there are now about 25. Hedge funds are interested in investing in marijuana businesses. Companies making components that can be used to smoke are now involved.

A movement once seen as fringe is now seen as something historic. As a result, the W.E.B. Du Bois Library at University of Massachusetts Amherst has started archiving NORML’s files, including many of St. Pierre’s personal papers. They have moved 200 cartons, 7,500 pounds, and thousands of videos.

The college, St. Pierre said, “is going to be the repository to answer the question for historians: How did marijuana become legal in the United States?”